Of recent interest are the identification and explanation of the residual learning and retention capacities that are found in amnesic patients with different etiologies. In spite of their severe amnesia, patients can learn, and retain for long periods of time, certain visuo-motor and even perceptual tasks. This strongly implies the existence of neural brain systems that can mediate unimpaired learning and retention in the absence of memory systems. Our specific aims are: 1. To identify, in the monkey, one of the brain systems that may mediate object-reward learning (associative form of learning with repeated trials) 2. Once identified, to dissociate the effects of lesions within that system from the effects of lesions that are known to impair recognition memory of trial-unique events (in both patients and monkeys). Our specific hypotheses to be tested are: a. Lesions within the mesolimbic reward system will impair object-reward association learning with repeated trials, but not recognition memory for trial-unique events. b. Lesions of the hippocampus (bitemporal amnesia) or those of the medial-dorsal thalamus (diencephalic amnesia), known to impair memory, will not impair object- reward association learning. To test these hypotheses lesions will be made in the nucleus accumbens (part of the mesolimbic reward system) and the effects of these lesions will be compared and contrasted with those that follow lesions of the hippocampus or of the thalamic medial-dorsal nucleus. The performance of normal, control monkeys and that of operated monkeys will be assessed on the following tasks: The concurrent object discrimination, with either "massed" or "distributed" practice; The object-pair association memory task and on delayed non-matching to sample visual recognition task which assesses recognition of an object after only one previous experience with it.